Part 3: general characteristicsFundamental or characteristic. What's the difference?

Free from the notes: Sparky’s video on it, the section word for word as members see it, and a PDF to keep.

Watch · 2:03
The notes
Get the full notes

From Sparky’s full video lesson. Members get the whole lesson on every notes page.

The notes

Exactly as they are on the site.

Part 3 is assessment of general characteristics, and the exam loves it because the contents page does most of the work for you. First, the distinction that makes the whole part make sense:

≡Fundamental (Part 1)
What every installation has. Every installation has an earthing arrangement. Every installation has live conductors.

≠Characteristic (Part 3)
What makes yours different. Whether it's TT or TN-C-S. Whether it's 230 V or 400 V. The size and type of the incoming fuse.

An analogy that helps. Everyone who drives needs a licence — that's fundamental. What the licence lets you drive, car or motorbike, is the characteristic. Same with people: we all have a skeleton (fundamental); hair and skin colour are characteristics.

So 230 V nominal is a general characteristic, not a fundamental principle — an industrial site may need 400 V or 11 kV. Most people get this wrong first time.

Chapter	Covers	Keyword that sends you here
31	Purposes, supplies and structure — 311 maximum demand, 312 conductor arrangement and system earthing, 313 supplies, 314 division of an installation	"maximum demand", "number of final circuits"
32	External influences — but it sends you to Appendix 5	"external influence", "category code"
33	Compatibility	"compatibility of equipment"
34	Maintainability	"maintainability", "who shall be consulted"
35	Safety services	"recognised source for safety services"
36	Continuity of service	"continuity of service", "assessment for each circuit"

Part 3 also carries the system diagrams — TN-S, TN-C-S, TT and the rest, drawn as line diagrams with the supply, the load and the protective conductors. Worth knowing they're there, because "identify this system" questions are popular.

⚠Single phase two wire, three wire, two phase three wire… When the book counts "wires" here it means live conductors (line and neutral). The earth isn't in that count, even though you'll still have one.

A newer arrangement worth knowing about: PNB — protective neutral bonding — sitting alongside the familiar PME arrangement, with the neutral-earth link made at the consumer's side rather than the supply side. Expect to see more of it.

Chapter 30 · assessment of general characteristics Chapter 31 · purposes, supplies and structure Part 3 · system line diagrams (TN-S, TN-C-S, TT)

Free section from Sparky Study Notes. The full Level 3 notes, 1,463 practice questions and the video lessons: sparkystudynotes.co.uk

Test yourself on it

The tests are in the members’ area. Get one wrong and it shows you why, and where to revise.

Get access

Get new notes and exam tips from Sparky

About one email a fortnight. Unsubscribe any time. Privacy notice

That was one section. There are 583.

Sparky Study Notes is the whole Level 3 syllabus written up like this: the explanation, the worked example, and where it is in your book. With a video lesson for every part and a practice paper for every exam.

583sections of written notes
35video lessons
1,463practice questions
146diagrams, redrawn

18th Edition
Building Regs
PAT
Fundamental Inspection & Testing
Initial Verification
Periodic Inspection & Testing

Get access — £100 12 months. One payment. See what’s inside